Communication network system, and transmission/reception apparatus, method and integrated circuit for use therein

ABSTRACT

A communication network system sets communication parameters which enable an operation under a maximum possible communication rate in a situation where a transmission path has cyclic noise/impedance fluctuations. A transmission/reception apparatus  100  transmits training packets for checking the state of the power line at two distinct points in time. A transmission/reception apparatus analyzes SNR at each carrier frequency, and stores an SNR evaluation result. The transmission/reception apparatus compares two SNR evaluation results which are obtained through two instances of a channel estimation algorithm, selects an SNR evaluation result which dictates a faster PHY rate, and transmits it to the transmission/reception apparatus. The transmission/reception apparatus changes modulation/demodulation rules based on the received SNR analytical result.

This application is a divisional application of application Ser. No.10/895,379, filed Jul. 21, 2004 now U.S. Pat. No. 7,684,502.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication network system whichcan perform data transmissions so as to be adaptable to changes in thestate of a transmission path, as well as a transmission/receptionapparatus, a method, and an integrated circuit for use therein. Moreparticularly, the present invention relates to a communication networksystem which employs a power line as a transmission path, as well as atransmission/reception apparatus, a method, and an integrated circuitfor use therein.

2. Description of the Background Art

As communication network systems which realize data transmissions so asto be adaptable to the changing states of a transmission path bymonitoring the state of the transmission path, wireless LAN systems andpower line communication systems have been put to practical use.

As a wireless LAN system, IEEE 802.11b using 2.4 GHz, and IEEE 802.11ausing 5 GHz are standardized, and are widely prevalent. Theabove-described wireless LAN systems employ a fall down algorithm bywhich an appropriate modulation method is selected from among differenttypes of modulation methods in accordance with transmission conditions.The fall down algorithm reduces a communication speed in accordance withtransmission conditions. IEEE 802.11a provides 54 Mbps transmissionspeed by using 64 QAM, but its communication range and noise immunityare substantially inferior to a modulation method such as 16 QAM. Thus,the wireless LAN system changes a modulation method according totransmission conditions, thereby continuing communication.

On the other hand, HomePlug1.0, which is a standard of a communicationsystem by which 14 Mbps communication is realized by using a home powerline, is developed by HomePlug Powerline Alliance, and is in practicaluse (see Sobia Baig et al., “A Discrete Multitone Transceiver at theHeart of the PHY Layer of an In-Home Power Line Communication Local AreaNetwork”, IEEE Communication Magazine, April 2003, pp. 48-53).

FIG. 13 is a block diagram showing a structure of atransmission/reception apparatus 90 defined by HomePlug1.0. In FIG. 13,the transmission/reception apparatus 90 includes a transmitting-endcommunication control section 91, a plurality of QAM encoder sections92, an IFFT section 93, an AFE (Analog Front End) 94, an FFT section 95,a plurality of QAM decoder sections 96, a receiving-end communicationcontrol section 97, and an SNR analytical results/acknowledgementnotifying section 98.

The transmitting-end communication control section 91 determines how toallocate a bit string of input data to the QAM encoder section(s) 92based on SNR analytical results notified by the SNR analyticalresults/acknowledgement notifying section 98. The transmitting-endcommunication control section 91 allocates a bit string of input data toeach QAM encoder section 92 in accordance with an allocation schemedetermined based on the SNR analytical results. That is, thetransmitting-end communication control section 91 performsserial-to-parallel conversion for input data in accordance with anallocation scheme determined based on the SNR analytical results. Thetransmitting-end communication control section 91, which is providedwith a buffer for temporarily storing input data, temporarily storesinput data in the buffer. Then, the transmitting-end communicationcontrol section 91 performs serial-to-parallel conversion for thetemporarily stored input data, and outputs the converted data. In thecase where transmitted data is not received successfully, thetransmitting-end communication control section 91 retransmits thetemporarily stored input data in accordance with an acknowledgementnotified by the SNR analytical results/acknowledgement notifying section98.

A transmitting-end transmission/reception apparatus and a receiving-endtransmission/reception apparatus perform a process for changing a bitallocation scheme based on the SNR analytical results in a coordinatedmanner. Specifically, the transmitting-end transmission/receptionapparatus transmits a training packet to the receiving-endtransmission/reception apparatus. In response to this, the receiving-endtransmission/reception apparatus analyzes an SNR (Signal to Noise Ratio)of each carrier based on the transmitted training packet. Theabove-described SNR of each carrier is sent back to the transmitting-endtransmission/reception apparatus as SNR analytical results. Based on thetransmitted SNR analytical results, the transmitting-endtransmission/reception apparatus determines a bit number allocated toeach carrier. Hereinafter, the above-described process is referred to asa training session.

Each QAM encoder section 92 converts a bit string input from thetransmitting-end communication control section 91 to an amplitude valueand a phase value by using QAM (Quadratture Amplitude Modulation).

The IFFT section 93 executes an inverse Fourier transform based on theamplitude value and the phase value input from each QAM encoder section92, and outputs its results. Thus, an OFDM signal modulated inaccordance with the input data is output. The above-described OFDMsignal is transmitted to another transmission/reception apparatus viathe AFE 94.

The FFT section 95 performs a Fourier transform for the OFDM signalreceived from another transmission/reception apparatus via the AFE 94,and outputs an amplitude value and a phase value of each carrier.

Each QAM decoder section 96 demodulates the amplitude value and thephase value, which is output from the FFT section 95, back into a bitstring by using QAM, and outputs the bit string.

The receiving-end communication control section 97 converts the bitstring output from each QAM decoder section 96 to a continuous bitstring, and outputs the continuous bit string as output data. That is,the receiving-end communication control section 97 performsserial-to-parallel conversion, thereby outputting output data. Also, thereceiving-end communication control section 97 analyzes an SNR of eachcarrier based on the amplitude value and the phase value output fromeach QAM decoder 96 during the training session. The receiving-endcommunication control section 97 notifies the SNR analytical results tothe transmitting-end communication control section 91 via the SNRanalytical results/acknowledgement notifying section 98. Thereceiving-end communication control section 97 checks whether or not allpackets transmitted from the transmitting-end transmission/receptionapparatus are received successfully based on the generated output data.The above-described checking process is referred to an acknowledgement.The receiving-end communication control section 97 notifiesacknowledgement results to the transmitting-end communication controlsection 91 via the SNR analytical results/acknowledgement notifyingsection 98.

The transmission/reception apparatus 90 shown in FIG. 13, which iscompliant with HomePlug1.0, divides a data string into a large number oflow rate data, and allocates the divided data to a large number ofsub-carriers, each of which is orthogonal to others, for transmission.The receiving-end communication control section 97 uses a channelestimation algorithm, which is executed during a training session, formeasuring an SNR in accordance with a specific frame transmitted from atransmission end. The channel estimation algorithm changes a modulationspeed by estimating channel conditions. By conventional HomePlug1.0specifications, a plurality of sub-carriers are modulated in a similarmanner by selecting a single modulation parameter. However, newlyperformed researches have revealed that further speeding-up is realizedusing a method called DMT (Discrete Multitone), by which a bit number tobe allocated to each carrier is determined by the transmitting-endcommunication control section 91 in accordance with each carrier's SNRfed back thereto.

FIGS. 14A to 14C are illustrations for describing a basic concept ofDMT. In FIG. 14A, sub-carriers are denoted by numerals 1 to n, ahorizontal axis indicates a frequency, and a vertical axis indicates abit number (i.e., modulation level) allocated to each carrier. FIG. 14Ashows that the sub-carriers are in the same state.

FIG. 14B is an illustration showing an exemplary SNR analyzed at thereceiving end. In FIG. 14B, a horizontal axis indicates a frequency, anda vertical axis indicates an SNR value.

In the case of the SNR as shown in FIG. 14B, the transmitting-endcommunication control section 91 allocates a greater number of bit to asub-carrier with a frequency of higher SNR values, and does not allocateany bit to a sub-carrier with SNR values smaller than a predeterminedthreshold value (SNR threshold), as shown in FIG. 14C. As such, thetransmitting-end communication control section 91 controls the bitallocation scheme applied to the QAM encoder sections 92 based on theSNR analytical results, thereby changing a modulation method to transmitdata without transmission errors.

The SNR is decreased by the following factors, for example: loadconditions depending on a status of a device connected to a power line,noise, narrow-band noise of an amateur radio and a short-wave radio,etc., and attenuation of a signal (see Jose Abad et al., “Extending thePower Line LAN Up to the Neighborhood Transformer”, IEEE CommunicationsMagazine, April 2003, pp. 64-70). The above-described factors change inaccordance with wiring conditions, and a connection status or anoperation status of a device. The factors may change on aminute-by-minute, hour-by-hour, day-by-day, or year-by-year basis.

In the conventional wireless LAN system and the power line communicationsystem, a modulation parameter is adaptively changed by the fall downalgorithm, the channel estimation algorithm, or the like. As such, atransmission speed is adjusted so as to avoid errors, thereby achievingthe maximum throughput under the current transmission conditions.

In the above-described systems, a training session may be performedbefore communication is started. During the training session, it isnecessary to perform a sequence of processes such that a specific packet(a test packet) is transmitted from a transmitting end, and a feedbackpacket (SNR analytical results) is sent back from a receiving end. Thus,frequent training sessions increase overhead, whereby communicationspeed is reduced irrespective of transmission conditions. In order toavoid such reduction in communication speed, a training session may beperformed at regular intervals, for example, in a cycle of five seconds.However, the channel conditions and the above-described cycle are notsynchronized. As a result, if the channel conditions change during acycle, communication is interrupted until a next cycle is started. Inthe case where a training session is performed in a cycle of fiveseconds, for example, communication may be interrupted as much as fiveseconds in the worst case. Thus, even when a training session is beingperformed at regular intervals, a cycle thereof may be changed to anirregular cycle in the case where communication conditions are degradeddue to a change in channel conditions.

In either one of the above cases, a transmitting end sends a specificpacket only once during a training session, and a receiving end returnsa feedback packet only once, which gives rise to the following problems.

In a power line communication system, noise and impedance fluctuates insynchronization with a supply power cycle or half the supply powercycle. For example, in the case where the supply power cycle is 50 Hz,the noise and impedance will have a fluctuation cycle of 20 msec or 10msec. In the case where the supply power cycle is 60 Hz, the noise andimpedance will have a fluctuation cycle 16.7 msec or 8.3 msec.

Noise which is in synchronization with the supply power cycle or halfthe supply power cycle of a home appliance, and impedance fluctuationsduring a supply power cycle of a half- or full-wave rectifier circuit ina home appliance are causes of noise/impedance fluctuations.Noise/impedance fluctuations occur locally, in the neighborhood of theresponsible home appliance or the like. In particular, it has been foundthat large fluctuations in noise and impedance may be ascribable to arecharger for a cellular phone, an electric carpet heater, or the like.Since these devices are in wide use at general households, it isnecessary to devise countermeasures against the fluctuations intransmission path characteristics caused by such devices, in order to beable to transmit AV (Audio Visual) signals, which require low-delay andlow-jitter characteristics.

FIG. 15 is a graph showing temporal changes in the phase of a signalwhich is transmitted over a power line to which an electric carpetheater is connected. As shown in FIG. 15, in accordance with theimpedance fluctuations of the power line due to a half-wave rectifiercircuit provided in the electric carpet heater, the phase of the signalbeing transmitted over the power line is fluctuating with a cycle ofabout 8 msec.

FIG. 16 is a graph showing measurement results of SNR of each carrier,obtained through channel estimation in the presence of power lineimpedance fluctuations as shown in FIG. 15. FIG. 16 show fluctuations inthe measurement results of SNR of each carrier which are obtainedthrough channel estimation in the presence of power line impedancefluctuations. A frame in which the SNR shows a maximum value is a framewhich is transmitted at a point in time where the phase of the signalbeing transmitted over the power line is not fluctuating. A frame inwhich the SNR shows a minimum value is a frame which is transmitted at apoint in time where the phase of the signal being transmitted over thepower line is fluctuating. There is a maximum difference of 20 dB in theSNR of sub-carrier numbers 120 to 200 (corresponding to frequencies of10 to 15 MHz) between the frame transmitted when the phase of the signalbeing transmitted over the power line is fluctuating and the frametransmitted when the phase of the signal being transmitted over thepower line is not fluctuating. Thus, there can be as much as 20 dB ofSNR fluctuations, depending on whether or not the point in time where achannel estimation is performed coincides with the point in time wherethe phase characteristics undergo a great fluctuation.

Next, the relationship between SNR evaluation results and communicationrates will be discussed. FIG. 17 is a table which shows off-linesimulation results of communication rates in the physical layer(hereinafter referred to as “PHY rates”), with respect to a maximum SNRand a minimum SNR, in the case where a channel to be used and amodulation level are selected based on a channel estimation.

As shown in FIG. 17, there is a difference of 30 Mbps between the PHYrate selected for the case where the SNR is maximum and the PHY rateselected for the case where the SNR is minimum. Therefore, in theconventional technique where a channel estimation is performed only onceduring a training session, if the transmission timing for an estimationrequest packet coincides with a phase-fluctuating moment, a PHY ratewhich is based on the minimum SNR will be selected. In this case, thecommunication efficiency is deteriorated because, during a period wherethe phase is not fluctuating, a transmission rate which is 30 Mbpsslower than an actually available PHY rate is being used.

SUMMARY OF THE INVENTION

Therefore, an aspect of the present invention is to provide acommunication network system which can set communication parameterswhich enable an operation under a maximum possible communication rate ina situation where a transmission path has cyclic and local noise and/orcyclic and local impedance fluctuations, without being influenced bysuch local noise/impedance fluctuations; and a transmission/receptionapparatus, a method, and an integrated circuit for use therein.

The present invention has the following aspects. The present inventionis directed to a transmission/reception apparatus for transmitting asignal which is modulated based on input data to another apparatus on acommunication network, and receiving a signal from another apparatus onthe communication network and demodulating the received signal. Thetransmission/reception apparatus comprises a multicarrier-modulationtransmission section for modulating a plurality of carriers havingrespectively different frequencies based on the input data, andtransmitting the modulated signal to another apparatus on thecommunication network; a multicarrier reception/demodulation section forreceiving a multicarrier-modulated signal transmitted from anotherapparatus on the communication network and demodulating themulticarrier-modulated signal; and a control section for, if apredetermined activation condition is satisfied, communicating withanother apparatus on the communication network acting as a counterpartof communication, executing two or more instances of a channelestimation algorithm for evaluating transmission quality on atransmission path with respect to a frequency of each carrier, andcontrolling, based on the transmission quality evaluated through the twoor more instances of the channel estimation algorithm executed, a set ofmodulation/demodulation rules to be used in the multicarrier-modulationtransmission section and the multicarrier reception/demodulationsection, wherein a time interval between two adjacent instances of thechannel estimation algorithm to be executed is unequal to a cycle ofquality fluctuation on the transmission path.

Preferably, in each instance of the channel estimation algorithm, thecontrol section derives, as an evaluation result of transmission qualityon the transmission path with respect to the frequency of each carrier,a set of modulation/demodulation rules for the multicarrier-modulationtransmission section and the multicarrier reception/demodulation sectionenabling transmission or reception of the signal without deteriorationin the transmission quality. The control section calculates acommunication rate in a physical layer to be obtained when using eachset of modulation/demodulation rules, and selects one of the sets ofmodulation/demodulation rules that dictates a maximum communication rateas the set of modulation/demodulation rules to be used in themulticarrier-modulation transmission section and the multicarrierreception/demodulation section.

For example, in each instance of the channel estimation algorithm, thecontrol section evaluates transmission quality on the transmission pathby determining a signal-to-noise ratio on the transmission path withrespect to the frequency of each carrier, and derives a set ofmodulation/demodulation rules for the multicarrier-modulationtransmission section and the multicarrier reception/demodulation sectionby allocating, for any carrier having a signal-to-noise ratio which isequal to or greater than a predetermined threshold value, a modulationlevel which is in accordance with the value of the signal-to-noiseratio, and by ensuring that any carrier having a signal-to-noise ratiowhich is less than the predetermined threshold value is not used, basedon the modulation level for each carrier. The control section calculatesthe communication rate to be obtained when using each set ofmodulation/demodulation rules, and selects one of the sets ofmodulation/demodulation rules that dictates a maximum communication rateas the set of modulation/demodulation rules to be used in themulticarrier-modulation transmission section and the multicarrierreception/demodulation section.

Preferably, in each instance of the channel estimation algorithm, thecontrol section derives, as an evaluation result of transmission qualityon the transmission path with respect to the frequency of each carrier,a set of modulation/demodulation rules for the multicarrier-modulationtransmission section and the multicarrier reception/demodulation sectionenabling transmission or reception of the signal without deteriorationin the transmission quality. The control section calculates a throughputto be provided for an upper layer when using each set ofmodulation/demodulation rules, and selects one of the sets ofmodulation/demodulation rules that dictates a maximum throughput as theset of modulation/demodulation rules to be used in themulticarrier-modulation transmission section and the multicarrierreception/demodulation section.

For example, in each instance of the channel estimation algorithm, thecontrol section evaluates transmission quality on the transmission pathby determining a signal-to-noise ratio on the transmission path withrespect to the frequency of each carrier, and derives a set ofmodulation/demodulation rules for the multicarrier-modulationtransmission section and the multicarrier reception/demodulation sectionby allocating, for any carrier having a signal-to-noise ratio which isequal to or greater than a predetermined threshold value, a modulationlevel which is in accordance with the value of the signal-to-noiseratio, and by ensuring that any carrier having a signal-to-noise ratiowhich is less than the predetermined threshold value is not used. Thecontrol section causes the multicarrier-modulation transmission sectionto actually transmit a signal by using each of the derived sets ofmodulation/demodulation rules, calculates the throughput for each set ofmodulation/demodulation rules based on a data retransmission rate, andselects one of the sets of modulation/demodulation rules that dictates amaximum throughput as the set of modulation/demodulation rules to beused in the multicarrier-modulation transmission section and themulticarrier reception/demodulation section.

Preferably, the control section includes: PHY ratemodulation/demodulation rules determination means for deriving, in eachinstance of the channel estimation algorithm, as an evaluation result oftransmission quality on the transmission path with respect to thefrequency of each carrier, a set of modulation/demodulation rules forthe multicarrier-modulation transmission section and the multicarrierreception/demodulation section enabling transmission or reception of thesignal without deterioration in the transmission quality. The controlsection calculates a communication rate in a physical layer to beobtained when using each of the derived sets of modulation/demodulationrules, and selects one of the sets of modulation/demodulation rules thatdictates a maximum communication rate as the set ofmodulation/demodulation rules to be used in the multicarrier-modulationtransmission section and the multicarrier reception/demodulationsection. The control section includes a MAC rate modulation/demodulationrules determination means for deriving, in each instance of the channelestimation algorithm, as an evaluation result of transmission quality onthe transmission path with respect to the frequency of each carrier, aset of modulation/demodulation rules for the multicarrier-modulationtransmission section and the multicarrier reception/demodulation sectionenabling transmission or reception of the signal without deteriorationin the transmission quality. The control section calculates a throughputto be provided for an upper layer when using each of the derived sets ofmodulation/demodulation rules, and selects one of the sets ofmodulation/demodulation rules which dictates a maximum throughput as theset of modulation/demodulation rules to be used in themulticarrier-modulation transmission section and the multicarrierreception/demodulation section. The control section also includes ameans for, based on a predetermined condition, switching betweenselecting the set of modulation/demodulation rules to be used byemploying the PHY rate modulation/demodulation rules determination meansor selecting the set of modulation/demodulation rules to be used byemploying the MAC rate modulation/demodulation rules determinationmeans.

Preferably, the control section retransmits data if the data is notcorrectly received by the other apparatus acting as the counterpart ofcommunication.

In a preferred embodiment, the transmission path is a power line towhich commercial electric power is applied, and the time intervalbetween two adjacent instances of the channel estimation algorithm to beexecuted is unequal to an integer multiple of a cycle of the commercialelectric power and unequal to an integer multiple of half the cycle ofthe commercial electric power.

Preferably, the control section further comprises transmission qualityevaluation means for, in response to a channel estimation algorithmexecuted by the other apparatus on the communication network acting asthe counterpart of communication, evaluating transmission quality on thetransmission path with respect to the frequency of each carrier, andreturning a result of each evaluation to the other apparatus.

Preferably, based on the evaluation of the transmission quality on thetransmission path with respect to the frequency of each carrier, thetransmission quality evaluation means derives a set ofmodulation/demodulation rules for each instance of the channelestimation algorithm, calculates a communication rate in a physicallayer to be obtained when using each of the sets ofmodulation/demodulation rules, and returns one of the sets ofmodulation/demodulation rules that dictates a maximum communication rateto the other apparatus.

Preferably, based on evaluation results of transmission quality on thetransmission path with respect to the frequency of each carrier which issent from the other apparatus on the communication network acting as thecounterpart of communication in response to each instance of the channelestimation algorithm, the control section derives a set ofmodulation/demodulation rules for each instance of the channelestimation algorithm, calculates a communication rate in a physicallayer to be obtained when using each of the sets ofmodulation/demodulation rules, and selects one of the sets ofmodulation/demodulation rules that dictates a maximum communication rateas the set of modulation/demodulation rules to be used in themulticarrier-modulation transmission section and the multicarrierreception/demodulation section.

Moreover, the present invention is directed to a communication networksystem for allowing a signal which is modulated based on input data tobe transmitted or received between first and secondtransmission/reception apparatuses. The first transmission/receptionapparatus comprising: a first multicarrier-modulation transmissionsection for modulating a plurality of carriers having respectivelydifferent frequencies based on the input data, and transmitting themodulated signal to the second transmission/reception apparatus; a firstmulticarrier reception/demodulation section for receiving anddemodulating the multicarrier-modulated signal transmitted from thesecond transmission/reception apparatus; and a first control sectionfor, if a predetermined activation condition is satisfied, communicatingwith the second transmission/reception apparatus, executing two or moreinstances of a channel estimation algorithm for evaluating transmissionquality on a transmission path with respect to a frequency of eachcarrier, and controlling, based on the transmission quality evaluatedthrough the two or more instances of the channel estimation algorithmexecuted, a set of modulation/demodulation rules to be used in the firstmulticarrier-modulation transmission section and the first multicarrierreception/demodulation section. The second transmission/receptionapparatus comprising: a second multicarrier-modulation transmissionsection for modulating a plurality of carriers having respectivelydifferent frequencies based on the input data, and transmitting themodulated signal to the first transmission/reception apparatus; a secondmulticarrier reception/demodulation section for receiving anddemodulating the multicarrier-modulated signal transmitted from thefirst transmission/reception apparatus; and a second control sectionfor, in response to the channel estimation algorithm executed by thefirst transmission/reception apparatus, evaluating transmission qualityon the transmission path with respect to the frequency of each carrierand returning a result of each evaluation to the firsttransmission/reception apparatus, wherein a time interval between twoadjacent instances of the channel estimation algorithm to be executed isunequal to a cycle of quality fluctuation on the transmission path.

Moreover, the present invention is directed to a method for determininga set of modulation/demodulation rules to be used in first and secondtransmission/reception apparatuses for transmitting or receiving amulticarrier-modulated signal on a communication network, comprising: astep performed through a cooperation of the first transmission/receptionapparatus and the second transmission/reception apparatus of, if apredetermined activation condition is satisfied, executing two or moreinstances of a channel estimation algorithm for evaluating transmissionquality on a transmission path in the communication network with respectto a frequency of each carrier, and a step of determining, based on thetransmission quality evaluated through the two or more instances of thechannel estimation algorithm executed, a set of modulation/demodulationrules to be used for multicarrier modulation/demodulation, wherein atime interval between two adjacent instances of the channel estimationalgorithm to be executed is unequal to a cycle of quality fluctuation onthe transmission path.

Moreover, the present invention is directed to an integrated circuit tobe used in a transmission/reception apparatus for transmitting a signalwhich is modulated based on input data to another apparatus on acommunication network, and receiving a signal from another apparatus onthe communication network and demodulating the received signal. Theintegrated circuit comprises a multicarrier-modulation transmissionsection for modulating a plurality of carriers having respectivelydifferent frequencies based on the input data, and transmitting themodulated signal to another apparatus on the communication network; amulticarrier reception/demodulation section for receiving amulticarrier-modulated signal transmitted from another apparatus on thecommunication network and demodulating the multicarrier-modulatedsignal; and a control section for, if a predetermined activationcondition is satisfied, communicating with another apparatus on thecommunication network acting as a counterpart of communication,executing two or more instances of a channel estimation algorithm forevaluating transmission quality on a transmission path with respect tothe frequency of each carrier, and controlling, based on thetransmission quality evaluated through the two or more instances of thechannel estimation algorithm executed, a set of modulation/demodulationrules to be used in the multicarrier-modulation transmission section andthe multicarrier reception/demodulation section, wherein a time intervalbetween two adjacent instances of the channel estimation algorithm to beexecuted is unequal to a cycle of quality fluctuation on thetransmission path.

Moreover, the present invention is directed to a program for controllinga computer to determine a set of modulation/demodulation rules to beused in first and second transmission/reception apparatuses fortransmitting or receiving a multicarrier-modulated signal on acommunication network, comprising: a step performed through acooperation of the first transmission/reception apparatus and the secondtransmission/reception apparatus of, if a predetermined activationcondition is satisfied, executing two or more instances of a channelestimation algorithm for evaluating transmission quality on atransmission path in the communication network with respect to afrequency of each carrier, and a step of determining, based on thetransmission quality evaluated through the two or more instances of thechannel estimation algorithm executed, a set of modulation/demodulationrules to be used for multicarrier modulation/demodulation, wherein atime interval between two adjacent instances of the channel estimationalgorithm to be executed is unequal to a cycle of quality fluctuation onthe transmission path.

According to the present invention, two or more instances of a channelestimation algorithm are executed, such that a time interval betweenadjacent instances of the channel estimation algorithm to be executed isunequal to a cycle of quality fluctuations on a transmission path.Therefore, modulation rules which are based on the transmission qualityas evaluated by one of the instances of the channel estimation algorithmcan provide a maximum possible communication rate or throughput even inthe presence of cyclic and local noise or cyclic and local impedancefluctuations.

By determining the modulation rules so that the communication rate inthe physical layer (PHY rate) is maximized, it becomes possible toobtain a maximum communication rate even in the presence of cyclic andlocal noise or cyclic and local impedance fluctuations.

By determining the modulation rules so that a throughput (MAC rate) tobe provided for an upper layer is maximized, it becomes possible totransfer data with minimum errors, thus improving the communicationefficiency.

By switching between modulation rules which dictate a maximum PHY rateand modulation rules which dictate a maximum MAC rate as necessary, itbecomes possible to, for example, employ modulation rules which dictatea maximum PHY rate at usual times, and switch to modulation rules whichdictate a maximum MAC rate in the case where the transmission pathcharacteristics have deteriorated and a high retransmission rate exists.Thus, the modulation rules can be flexibly changed.

By providing a data retransmission function, it becomes possible toovercome transmission errors which occur due to the used carriers andmodulation parameters not being suited to cyclic noise or impedancefluctuations.

In the case where a power line to which commercial electric power isapplied is used as the transmission path, by ensuring that a timeinterval between two adjacent instances of the channel estimationalgorithm to be executed is not equal to an integer multiple of thecycle of the commercial electric power or half the cycle of thecommercial electric power, it becomes possible to provide a maximumpossible communication rate or throughput even in the presence ofnoise/impedance fluctuations which cyclically occur in accordance withthe supply power cycle.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the structure of a communicationnetwork system according to a first embodiment of the present invention,and the structure of transmission/reception apparatuses used in thecommunication network system;

FIG. 2 is a flowchart illustrating an operation of atransmission/reception apparatus which transmits training packets duringa training session;

FIG. 3 is a flowchart illustrating an operation of atransmission/reception apparatus which receives training packets duringa training session;

FIG. 4A is a sequence diagram illustrating a flow of processes between atransmission/reception apparatus which transmits training packets and atransmission/reception apparatus which receives the training packetsduring a training session;

FIG. 4B is a sequence diagram illustrating a flow of processes between atransmission/reception apparatus which transmits training packets and atransmission/reception apparatus which receives the training packetsduring a training session;

FIG. 4C is a sequence diagram illustrating a flow of processes between atransmission/reception apparatus which transmits training packets and atransmission/reception apparatus which receives the training packetsduring a training session;

FIG. 5 is a block diagram illustrating the structure oftransmission/reception apparatuses in the case where a Wavelet functionis employed;

FIG. 6 is a flowchart illustrating an operation of atransmission/reception apparatus according to a second embodiment of thepresent invention;

FIG. 7 is a sequence diagram illustrating a flow of processes performedin a communication network system according to a third embodiment of thepresent invention;

FIG. 8 is a flowchart illustrating an operation of a transmitting-endtransmission/reception apparatus in the case where the apparatusswitches between a training session for selecting a tone map whichdictates a maximum PHY rate and a training session for selecting a tonemap which dictates a maximum MAC rate;

FIG. 9A is a graph illustrating the effects obtained by performing twochannel estimations;

FIG. 9B is a graph illustrating the effects obtained by performing threeor more channel estimations;

FIG. 9C is a graph illustrating the effects obtained by performing threeor more channel estimations;

FIG. 10 is a flowchart illustrating an operation of atransmission/reception apparatus which transmits training packets duringa training session according to a fourth embodiment of the presentinvention;

FIG. 11 is a flowchart illustrating an operation of atransmission/reception apparatus which receives training packets duringa training session according to a fourth embodiment of the presentinvention;

FIG. 12 is a diagram illustrating the overall system structure in thecase where the transmission/reception apparatuses according to thepresent invention are applied to high-speed power line transmission;

FIG. 13 is a block diagram showing a structure of atransmission/reception apparatus 90 defined by HomePlug1.0;

FIG. 14A is an illustration for describing a basic concept of DMT;

FIG. 14B is an illustration for describing a basic concept of DMT;

FIG. 14C is an illustration for describing a basic concept of DMT;

FIG. 15 is a graph showing temporal changes in the phase of a signalwhich is transmitted over a power line to which an electric carpetheater is connected;

FIG. 16 is a graph showing measurement results of SNR of each carrier,obtained through channel estimation in the presence of power lineimpedance fluctuations as shown in FIG. 15; and

FIG. 17 is a table which shows off-line simulation results ofcommunication rates in the physical layer (PHY rates), with respect to amaximum SNR and a minimum SNR, in the case where a channel to be usedand a modulation level are selected based on a channel estimation.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the accompanying figures.

First Embodiment

FIG. 1 is a block diagram illustrating the structure of a communicationnetwork system according to a first embodiment of the present invention,and the structure of transmission/reception apparatuses used in thecommunication network system. In FIG. 1, the communication networksystem comprises transmission/reception apparatuses 100 and 101, whichare connected to each other via a power line to which commercialelectric power is supplied. Although FIG. 1 illustrates an example wherethere are two transmission/reception apparatuses, it will be appreciatedthat three or more transmission/reception apparatuses may be employed.

The transmitting-end transmission/reception apparatus 100, whichtransmits packets based on input data, transmits training packets forchecking the state of the power line at two distinct points in timeduring a training session. Every time a training packet is transmitted,the receiving-end transmission/reception apparatus 101 to which thetraining packet is transmitted analyzes SNR, which represents atransmission quality on the power line with respect to the frequency ofeach carrier, and stores the result of the analysis as an SNR evaluationresult. In the first embodiment, during a training session, trainingpackets are transmitted at two points in time; therefore, thereceiving-end transmission/reception apparatus 101 obtains two SNRevaluation results. Hereinafter, the portion of a training session whichis associated with the transmission of one training packet andobtainment of one SNR evaluation result will be referred to as a“channel estimation algorithm”. The channel estimation algorithm is aprocess for evaluating the transmission quality on the power line withrespect to each carrier frequency. The receiving-endtransmission/reception apparatus 101 compares two SNR evaluation resultswhich are obtained from two instances of the aforementioned channelestimation algorithm, selects one of the SNR evaluation results thatdictates a greater (i.e., faster) total of modulation speeds of thecarriers (PHY rate), and transmits the selected one of the SNRevaluation results (hereinafter referred to as an “SNR analyticalresult”) back to the transmitting-end transmission/reception apparatus100. The SNR analytical result contains a tone map which describescarriers to be used so that signals can be transmitted and receivedwithout causing degradation in transmission quality, and modulationlevels for such carriers to be used. Based on the received SNRanalytical result, the transmitting-end transmission/reception apparatus100 changes the modulation method.

In FIG. 1, the transmission/reception apparatuses 100 and 101 eachinclude a transmitting-end communication control section 1, a pluralityof QAM encoder sections 2, an IFFT section 3, an AFE 4, an FFT section5, a plurality of QAM decoder sections 6, a receiving-end communicationcontrol section 7, an SNR analytical results/acknowledgement notifyingsection 8, and an SNR evaluation result storage section 9.

The plurality of QAM encoder sections 2 and the IFFT section 3 functionas a multicarrier-modulation transmission section for modulating aplurality of carriers having respectively different frequencies based oninput data, and transmitting, via the AFE 4, the modulated signal toanother transmission/reception apparatus (100 or 101) which is connectedto the power line.

The FFT section 5, and the QAM decoder sections 6 function as amulticarrier reception/demodulation section for receiving anddemodulating a multicarrier-modulated signal which is sent from anothertransmission/reception apparatus (100 or 101) via the power line and theAFE 4.

The transmitting-end communication control section 1, the receiving-endcommunication control section 7, the SNR analyticalresults/acknowledgement notifying section 8, and the SNR evaluationresult storage section 9 are control sections for controlling modulationrules to be used in the multicarrier-modulation transmission section anddemodulation rules to be used in the multicarrier reception/demodulationsection. The modulation rules and the demodulation rules will becollectively referred to as “modulation/demodulation rules”. Themodulation/demodulation rules define which carriers are to be used,which carriers are not to be used, modulation levels for used carriers,and the like.

Hereinafter, the functions of the respective functional blocks will bedescribed with respect to the case where the transmitting-endtransmission/reception apparatus 100 transmits data to the receiving-endtransmission/reception apparatus 101. Based on an SNR analytical resultnotified from the SNR analytical results/acknowledgement notifyingsection 8, the transmitting-end communication control section 1 of thetransmission/reception apparatus 100 determines how to allocate a bitstring of input data to the QAM encoder sections 2, and determinesmodulation parameters, e.g., modulation levels, in the QAM encodersections 2 to be used. Note that the input data as used herein iscontinuous data. Specifically, as shown in FIG. 14C, for any carrierwhose SNR is equal to or greater than a predetermined threshold value(SNR threshold), the transmitting-end communication control section 1 ofthe transmission/reception apparatus 100 assigns a modulation level,which is in accordance with the SNR value, to a QAM encoder section 2.On the other hand, for any carrier whose SNR is less than thepredetermined threshold value, the transmitting-end communicationcontrol section 1 controls a QAM encoder section 2 so as not to use thecarrier.

In accordance with an allocation scheme which is determined based on theSNR analytical result, the transmitting-end communication controlsection 1 of the transmission/reception apparatus 100 allocates the bitstring of input data to the QAM encoder sections 2. In other words, thetransmitting-end communication control section 1 subjects the input datato serial-to-parallel conversion in accordance with an allocation schemewhich is determined based on a tone map contained in the SNR analyticalresult. The transmitting-end communication control section 1 of thetransmission/reception apparatus 100 controls the QAM encoder sections 2in accordance with modulation parameters which are determined based onthe tone map contained in the SNR analytical result. The allocationscheme and the modulation parameters are the modulation rules.

The transmitting-end communication control section 1 of thetransmission/reception apparatus 100 includes a buffer for temporarilystoring input data, and uses this buffer to temporarily store inputdata. The transmitting-end communication control section 1 subjects thetemporarily stored input data to serial-to-parallel conversion, andoutputs the converted data. Based on an acknowledgement which is to benotified from the SNR analytical results/acknowledgement notifyingsection 8, the transmitting-end communication control section 1 of thetransmission/reception apparatus 100 determines whether the transmittedpacket has been correctly received. If the packet has not been correctlyreceived, the transmitting-end communication control section 1 of thetransmission/reception apparatus 100 retransmits the temporarily storedinput data.

During a training session, the transmitting-end communication controlsection 1 of the transmission/reception apparatus 100 executes thechannel estimation algorithm at two distinct points in time, and outputstraining packets at two points in time. Note that the training sessionis to be begun when it is found that acknowledgements for packets are nolonger being received due to a deteriorated communication state, or whena predetermined activation condition (e.g., a predetermined period haselapsed) is satisfied. The transmitting-end communication controlsection 1 of the transmission/reception apparatus 100 subjects eachtraining packet to serial-to-parallel conversion, and allocates theresults of the conversion to the QAM encoder sections 2. In the trainingsession, the transmitting-end communication control section 1 of thetransmission/reception apparatus 100 equally allocates the trainingpackets having been obtained through the serial-to-parallel conversionto the QAM encoder sections 2. It is ensured that the time intervalbetween two points of training packet transmission is asynchronous tothe cycle and asynchronous to half the cycle of the commercial electricpower. In other words, the time interval between two points of trainingpacket transmission is neither an integer multiple of the cycle of thecommercial electric power, nor an integer multiple of half the cycle ofthe commercial electric power. Stated otherwise, the time intervalbetween two adjacent instances of the channel estimation algorithm to beexecuted is unequal to the cycle of the quality fluctuations on thepower line, and is equal neither to an integer multiple of the cycle ofthe commercial electric power, nor to an integer multiple of half thecycle of the commercial electric power.

In accordance with the modulation rules which are designated by thetransmitting-end communication control section 1, each QAM encodersection 2 of the transmission/reception apparatus 100 or 101 convertsthe bit string which is input from the transmitting-end communicationcontrol section 1 to an amplitude value and a phase value for output, byusing a QAM technique.

The IFFT section 3 of the transmission/reception apparatus 100 or 101performs an inverse Fourier transform based on the amplitude value andphase value input from each QAM encoder section 2, and outputs a resultthereof. Thus, an OFDM signal which has been multicarrier-modulated inaccordance with the input data is output. The OFDM signal is transmittedfrom the AFE 4 to the transmission/reception apparatus 101, via thepower line.

The FFT section 5 of the transmission/reception apparatus 100 or 101applies a Fourier transform to the OFDM signal received via the AFE 4from the transmission/reception apparatus 101, and outputs the amplitudevalue and the phase value of each carrier.

In accordance with the demodulation rules designated by thereceiving-end communication control section 7, each QAM decoder section6 of the transmission/reception apparatus 100 or 101 demodulates theamplitude value and the phase value output from the FFT section 5 usinga QAM technique, and outputs the result as a bit string.

In accordance with the demodulation rules which are based on the SNRanalytical result, the receiving-end communication control section 7 ofthe transmission/reception apparatus 100 or 101 controls thedemodulation levels in the QAM decoder sections 6 to be used. Thereceiving-end communication control section 7 of thetransmission/reception apparatus 100 or 101 converts the bit stringsoutput from the QAM decoder sections 6 into a continuous bit string,which is output as output data. Specifically, as shown in FIG. 14C, forany carrier whose SNR is equal to or greater than a predeterminedthreshold value (SNR threshold), the receiving-end communication controlsection 7 of the transmission/reception apparatus 100 or 101 assigns ademodulation level which is in accordance with the SNR value to a QAMdecoder section 6. On the other hand, for any carrier whose SNR is lessthan the predetermined threshold value, the receiving-end communicationcontrol section 7 controls a QAM decoder section 6 so as not to use thecarrier.

The receiving-end communication control section 7 of thetransmission/reception apparatus 101 determines whether the output datahas been correctly received or not, and if the output data has beencorrectly received, passes an acknowledgement to the SNR analyticalresults/acknowledgement notifying section 8. In response, thetransmitting-end communication control section 1 of thetransmission/reception apparatus 101 returns the acknowledgement whichis notified from the SNR analytical results/acknowledgement notifyingsection 8 to the transmission/reception apparatus from which data hasbeen transmitted.

During the training session, with respect to the training packet whichis transmitted from the counterparting transmission/reception apparatus100, the receiving-end communication control section 7 of thetransmission/reception apparatus 101 analyzes SNR of the carriers basedon the amplitude value and phase value output from each QAM decodersection 6, and stores SNR evaluation results to the SNR evaluationresult storage section 9. Since two instances of the channel estimationalgorithm are executed and training packets are transmitted at twopoints in time during the training session, the receiving-endcommunication control section 7 of the transmission/reception apparatus101 stores two SNR evaluation results to the SNR evaluation resultstorage section 9. The receiving-end communication control section 7 ofthe transmission/reception apparatus 101 compares the two SNR evaluationresults stored in the SNR evaluation result storage section 9, selectsone of the SNR evaluation results that dictates a greater (i.e., faster)total of modulation speeds of the carriers, and passes the selected oneof the SNR evaluation results (as an “SNR analytical result”) to the SNRanalytical results/acknowledgement notifying section 8.

In response, the transmitting-end communication control section 1 of thetransmission/reception apparatus 101 returns the SNR analytical resultwhich is notified from the SNR analytical results/acknowledgementnotifying section 8 to the transmission/reception apparatus 100 fromwhich the training packet has been transmitted. In the calculation ofthe total of modulation speeds of the carriers based on the SNRevaluation results, the receiving-end communication control section 7 ofthe transmission/reception apparatus 101 firstly ascertains SNR for eachchannel from each SNR evaluation result, and determines a tone mapdescribing the carriers to be used and modulation methods for thecarriers to be used. Next, based on the carriers to be used and themodulation methods for the carriers to be used as described in the tonemap thus determined, the receiving-end communication control section 7of the transmission/reception apparatus 101 determines a modulationspeed for each carrier, and calculates the total of modulation speeds ofthe carriers. The total of modulation speeds of the carriers is the PHYrate when a modulation is performed by using the tone map. Then, thereceiving-end communication control section 7 of thetransmission/reception apparatus 101 selects one of the SNR evaluationresults which is associated with a greater (i.e., faster) total ofmodulation speeds of the carriers (PHY rate), and transmits the tone mapcorresponding to the selected SNR evaluation result to thetransmitting-end transmission/reception apparatus 100 as an SNRanalytical result.

The SNR analytical results/acknowledgement notifying section 8 of thetransmission/reception apparatus 101 passes the SNR analytical resultand the acknowledgement obtained from the receiving-end communicationcontrol section 7 to the transmitting-end communication control section1. Note that the “SNR analytical result” as used herein includes an SNRanalytical result which is generated within the transmission/receptionapparatus itself, as well as an SNR analytical result which has beensent from another transmission/reception apparatus. Also note that the“acknowledgement” as used herein includes an acknowledgement which isgenerated within the transmission/reception apparatus itself, as well asan acknowledgement which has been sent from anothertransmission/reception apparatus. The transmitting-end communicationcontrol section 1 of the transmission/reception apparatus 100 changesbit allocation to the QAM encoder sections 2 based on the SNR analyticalresult which has been sent from another transmission/receptionapparatus. The receiving-end communication control section 7 of thetransmission/reception apparatus 100 changes the demodulation scheme inthe QAM decoder sections 6 based on the SNR analytical result which hasbeen sent from another transmission/reception apparatus. Thetransmitting-end communication control section 1 of thetransmission/reception apparatus 101 sends the SNR analytical resultwhich has been generated in the transmission/reception apparatus 101itself to another transmission/reception apparatus. The transmitting-endcommunication control section 1 of the transmission/reception apparatus100 retransmits the input data based on the acknowledgement which hasbeen sent from another transmission/reception apparatus. Thetransmitting-end communication control section 1 of thetransmission/reception apparatus 101 sends the acknowledgement which hasbeen generated in the transmission/reception apparatus 101 itself toanother transmission/reception apparatus.

FIG. 2 is a flowchart illustrating an operation of atransmission/reception apparatus which transmits training packets duringa training session. Hereinafter, with reference to FIG. 2, an operationof the transmission/reception apparatus which transmits training packetsduring a training session will be described.

First, the transmitting-end communication control section 1 of thetransmitting-end transmission/reception apparatus (e.g., thetransmission/reception apparatus 100 shown in FIG. 1) sets atransmission cycle Ttr0 [seconds] as a time interval between a firsttraining packet to be transmitted and a second training packet to betransmitted (step S201). The transmission cycle Ttr0 [seconds] isneither an integer multiple of the cycle of the commercial electricpower nor an integer multiple of half the cycle of the commercialelectric power.

Next, the transmitting-end communication control section 1 sets atimeout time Ttot [seconds] (step S202). The timeout time Ttot [seconds]may be, for example, on the order of several hundred msec. Typically,the timeout time Ttot [seconds] is longer than the transmission cycleTtr0 [seconds]. The timeout time defines a timing with which thetransmitting-end transmission/reception apparatus retransmits a trainingpacket if an SNR analytical result is not received within apredetermined period of time.

Next, the transmitting-end communication control section 1 transmits afirst training packet (step S203). The first training packet hasidentification information added thereto, which can be used at areceiving end to confirm that it is a first training packet.

Next, the transmitting-end communication control section 1 resets andstarts a transmission cycle counter for measuring time to determinewhether a transmission cycle for the training packet has been reached ornot (step S204).

Next, by referring to the transmission cycle counter, thetransmitting-end communication control section 1 determines whether thetransmission cycle Ttr0 [seconds] has passed (step S205). Until thetransmission cycle Ttr0 [seconds] passes, the transmitting-endcommunication control section 1 repeats the process of step S205. If thetransmission cycle Ttr0 [seconds] has passed, the transmitting-endcommunication control section 1 proceeds to the process of step S206.

At step S206, the transmitting-end communication control section 1transmits a second training packet. The second training packet hasidentification information added thereto, which can be used at areceiving end to confirm that it is a second training packet.

Next, the transmitting-end communication control section 1 resets andstarts a timeout counter for measuring time to determine whether thetimeout time has passed or not (step S207).

Next, by referring to the timeout counter, the transmitting-endcommunication control section 1 determines whether the timeout time Ttot[seconds] has passed or not (step S208). If the timeout time Ttot[seconds] has passed, the transmitting-end communication control section1 returns to the processes of step S203 and the subsequent steps, andretransmits the first and second training packets. On the other hand, ifthe timeout time Ttot [seconds] has not passed yet, the transmitting-endcommunication control section 1 proceeds to the process of step S209.

At step S209, the transmitting-end communication control section 1determines whether the receiving-end communication control section 7 hasreceived an SNR analytical result from the counterpartingtransmission/reception apparatus and whether the received SNR analyticalresult has been notified to the SNR analytical results/acknowledgementnotifying section 8. If an SNR analytical result has not been notified,the transmitting-end communication control section 1 returns to theprocess of step S208. On the other hand, if an SNR analytical result hasbeen notified, the transmitting-end communication control section 1 endsthe process. Thereafter, based on the received SNR analytical result,the transmitting-end communication control section 1 allocates inputdata to the QAM encoder sections 2, and transmits packets.

FIG. 3 is a flowchart illustrating an operation of atransmission/reception apparatus which receives training packets duringa training session. Hereinafter, with reference to FIG. 3, an operationof the transmission/reception apparatus which receives training packetsduring a training session will be described.

Firstly, upon receiving the first training packet (step S210), thereceiving-end communication control section 7 of the receiving-endtransmission/reception apparatus begins the following operation. Thereceiving-end communication control section 7 determines, based on theidentification information added to the first training packet, whetherthe transmitted packet is the first training packet or not.

At step S211, the receiving-end communication control section 7evaluates the SNR of the first training packet for each carrier.

Next, the receiving-end communication control section 7 stores theevaluation result to the SNR evaluation result storage section 9 as afirst SNR evaluation result (step S212). The first SNR evaluation resultrepresents the carrier-to-carrier SNR of the first training packet.

Next, the receiving-end communication control section 7 sets a timeouttime Ttor [seconds] (step S213). The timeout time Ttor [seconds] may be,for example, on the order of several hundred msec. The reason forsetting the timeout time Ttor [seconds] is in order to ensure that, in asituation where the second training packet transmitted from thetransmitting end cannot be received for some reason, the receiving endtransitions from a state of waiting for the second training packet to anormal state where the receiving end transitions is able to receive thefirst training packet to be again transmitted from the transmitting end.

Next, the receiving-end communication control section 7 resets andstarts a timeout counter for measuring time to determine whether thetimeout time has passed or not (step S214).

Next, by referring to the timeout counter, the receiving-endcommunication control section 7 determines whether the timeout time Ttor[seconds] has passed or not (step S215). If the timeout time Ttor[seconds] has passed, the receiving-end communication control section 7ends the process. On the other hand, if the timeout time Ttor [seconds]has not passed yet, the receiving-end communication control section 7proceeds to the process of step S216.

At step S216, the receiving-end communication control section 7determines whether the second training packet is being received. Notethat the receiving-end communication control section 7 determineswhether the transmitted packet is the second training packet based onthe identification information added to the second training packet. Ifthe second training packet has not been received, the receiving-endcommunication control section 7 returns to the process of step S215. Onthe other hand, if the second training packet is being received, thereceiving-end communication control section 7 proceeds to the process ofstep S217.

At step S217, the receiving-end communication control section 7evaluates the SNR of the second training packet for each carrier.

Next, the receiving-end communication control section 7 stores theevaluation result to the SNR evaluation result storage section 9 as asecond SNR evaluation result (step S218). The second SNR evaluationresult represents the carrier-to-carrier SNR of the second trainingpacket.

Next, the receiving-end communication control section 7 determines afirst tone map based on the first SNR evaluation result stored in theSNR evaluation result storage section 9, and determines a second tonemap based on the second SNR evaluation result. The receiving-endcommunication control section 7 compares the first and second tone mapsand selects an SNR evaluation result which dictates a greater (i.e.,faster) total of modulation speeds of the carriers (PHY rate)(stepS219).

Next, the receiving-end communication control section 7 notifies thetone map corresponding to the SNR evaluation result selected at stepS219 to the SNR analytical results/acknowledgement notifying section 8,as an SNR analytical result. In response, the transmitting-endcommunication control section 1 transmits the SNR analytical result tothe transmission/reception apparatus from which the training packet hasbeen transmitted (step S220), and ends the process. Based on the SNRanalytical result thus sent, the transmission/reception apparatus whichhas transmitted the training packet allocates input data to the QAMencoder sections 2, and transmits the resultant packets.

In the processes shown in FIG. 2 and FIG. 3, steps S203 to S205 andsteps S210 to S215 are the first instance of the channel estimationalgorithm. Steps S206 to S209 and steps S216 to S220 are the secondinstance of the channel estimation algorithm.

FIGS. 4A, 4B, and 4C are sequence diagrams illustrating flows ofprocesses between a transmission/reception apparatus which transmitstraining packets and a transmission/reception apparatus which receivesthe training packets during a training session. In FIG. 4A to 4C, eachsquare box on a line indicating a flow of processes at the receiving endrepresents a period during which the characteristics of the transmissionpath fluctuates (hereinafter referred to as “transmission pathcharacteristics fluctuation time”). In the illustrated example, it isassumed that each transmission path characteristics fluctuation time isreached with an interval of 16.7 msec. RCE1PDU is a first channelestimation request packet containing a first training packet. ACKPDU isa packet indicating that a channel estimation request packet has beenproperly received. RCE2PDU is a second channel estimation request packetcontaining a second training packet. The transmission cycle Ttr0 betweenthe first channel estimation request packet and the second channelestimation request packet is 20 msec. CERPDU is a channel estimationreply packet containing the SNR analytical result. FIG. 4A illustrates aflow of processes to be performed in the case where the state of thetransmission path fluctuates at neither the point of transmitting thefirst training packet nor the point of transmitting the second trainingpacket. FIG. 4B illustrates a flow of processes to be performed in thecase where the state of the transmission path fluctuates at the point oftransmitting the first training packet. FIG. 4C illustrates a flow ofprocesses to be performed in the case where the state of thetransmission path fluctuates at the point of transmitting the secondtraining packet.

By using the first and second training packets contained in the firstand second channel estimation request packets, the receiving-endtransmission/reception apparatus evaluates the carrier-to-carrier SNReach time, and based on the first and second SNR evaluation results,determines the first and second tone maps describing carriers to be usedand modulation methods for the carriers to be used, etc.

As the SNR analytical result, the receiving-end transmission/receptionapparatus selects the tone map which dictates the greater PHY rate amongthe PHY rates obtained by performing modulation by using the first andsecond tone maps determined in response to the two channel estimationrequests, and returns a channel estimation reply packet containing theSNR analytical result to the transmitting-end transmission/receptionapparatus.

The transmission cycle Ttr0 between the first channel estimation requestpacket and the second channel estimation request packet must be set soas to be asynchronous to the cycle of the commercial electric power andasynchronous to half the cycle of the commercial electric power. Inother words, the transmission cycle Ttr0 is neither an integer multipleof the cycle of the commercial electric power nor an integer multiple ofhalf the cycle of the commercial electric power.

Thus, by ensuring that the transmission cycle Ttr0 is asynchronous tothe supply power cycle and asynchronous to half the supply power cycle,the tone maps obtained from both of RCE1PDU and RCE2PDU will dictatefast PHY rates in an exemplary case (as shown in FIG. 4A) where twotransmission path characteristics fluctuation times are reached betweenthe transmission of RCE1PDU and the transmission of RCE2PDU.

In an exemplary case (as shown in FIG. 4B) where the transmission pathcharacteristics fluctuation time coincides with the transmission ofRCE1PDU, the tone map obtained from RCE2PDU will dictate a faster PHYrate.

In an exemplary case (as shown in FIG. 4C) where the transmission pathcharacteristics fluctuation time coincides with the transmission ofRCE2PDU, the tone map obtained from RCE1PDU will dictate a faster PHYrate.

Thus, among the two channel estimation requests, it is possible toutilize the tone map which dictates a faster PHY rate. In other words,an SNR analytical result obtained at a point in time which is notencountered by a transmission path characteristics fluctuation isreturned to the transmitting end as a channel estimation reply packet.Therefore, it is possible to perform communications at a transmissionrate corresponding to the transmission path characteristics which existat normal times.

Thus, according to the first embodiment of the present invention, evenin the presence of cyclic and local noise, or cyclic and local impedancefluctuations, a decrease in the communication rate due to the use ofmodulation parameters associated with a low modulation speed can beprevented.

Note that, in the first embodiment, it is assumed that QAM is used as amodulation scheme, but it is not limited thereto. For example, BPSK,QPSK, PAM, or ASK modulation may be used as a modulation scheme. In thecase where PAM is used as a modulation scheme, thetransmission/reception apparatus will employ a DWT (Discrete WaveletTransform) section and an IDWT (Inverse Discrete Wavelet Transform)section, in which a Wavelet function is used as a basis function inplace of a trigonometric function in an FFT section and an IFFT section.FIG. 5 is a block diagram illustrating the structure oftransmission/reception apparatuses in the case where a Wavelet functionis employed. As shown in FIG. 5, in the case where PAM encoder sections2 a and PAM decoder sections 6 a are employed, an IDWT section 3 a and aDWT section 5 a are to be used. The effect of the present invention canalso be obtained in such cases.

The above embodiment illustrates a case where, based on SNR analyticalresults corresponding to two training packets, the receiving end selectsone analytical result and notifies it to the transmitting end. Anessence of the present invention lies in the fact that: two instances ofa channel estimation algorithm are executed with a time interval whichis unequal to the interval between instances of cyclic noise and/orcyclic impedance fluctuations; based on a channel estimation resultwhich dictates a faster total modulation speeds of the used carriers,the carrier to be used and/or the modulation parameter for each carrierare determined; and thereafter a communication is performed by using thecarriers and the modulation parameters for the respective carriers.Therefore, it would be possible for the receiving end to return both ofthe analytical results for the two training packets to the transmittingend, and the transmitting end may select an SNR analytical result.Alternatively, both the transmitting end and the receiving end mayselect an SNR analytical result. Similar effects can be obtained ineither case.

Second Embodiment

The transmission/reception apparatus according to the first embodimentprevents a decrease in the communication rate by performing two channelestimations and adopting one of the tone maps which dictates a fasterPHY rate. Therefore, at a point where cyclic noise or impedancefluctuations are occurring, the packets are likely to contain errors.Therefore, in a second embodiment of the present invention, a functionof retransmitting a packet to correct any packet which contains an erroris provided in addition to the functions provided according to the firstembodiment. The block structure of the transmission/reception apparatusof the second embodiment is identical to that in the first embodiment,and therefore FIG. 1 will be relied on in the following description.

FIG. 6 is a flowchart illustrating an operation of atransmission/reception apparatus according to the second embodiment ofthe present invention. Hereinafter, with reference to FIG. 6, anoperation of the transmission/reception apparatus according to thesecond embodiment of the present invention will be described.

First, the transmitting-end communication control section 1 sets atraining cycle Tt0 [seconds] defining a period during which to execute atraining session (step S501). Next, the transmitting-end communicationcontrol section 1 sets a threshold value Nr0 [times] for the number oftimes of retransmission (step S502). Then, the transmitting-endcommunication control section 1 resets and starts a training cycle timerTt [seconds] for counting training cycles (step S503). Next, thetransmitting-end communication control section 1 resets and starts aretransmitting times counter Nr [times] for counting the number of timesof retransmission (step S504).

Next, the transmitting-end communication control section 1 compares thetraining cycle timer Tt [seconds] against the training cycle Tt0[seconds] to determine whether the training cycle Tt0 [seconds] haspassed or not (step S505). If the training cycle Tt0 [seconds] has notpassed yet, the transmitting-end communication control section 1proceeds to the process of step S506. On the other hand, if the trainingcycle Tt0 [seconds] has passed, the transmitting-end communicationcontrol section 1 proceeds to the process of step S508.

At step S506, the transmitting-end communication control section 1compares the retransmitting times counter Nr [times] against theretransmitting times threshold value Nr0 [times] to determine whetherthe retransmitting times has reached the retransmitting times thresholdvalue, i.e., Nr=Nr0. If Nr=Nr0, the transmitting-end communicationcontrol section 1 proceeds to the process of step S508. On the otherhand, if Nr=Nr0 is not true, the transmitting-end communication controlsection 1 proceeds to the process of step S507.

At step S507, the transmitting-end communication control section 1transmits a packet, and returns to the process of step S505. If thepacket to be transmitted is a packet for which an acknowledgement hasnot been obtained, i.e., if the packet is for retransmission, thetransmitting-end communication control section 1 increments theretransmitting times counter Nr [times] by one (Nr=Nr+1), and returns tothe process of step S505.

At step S508, the transmitting-end communication control section 1performs a training session by transmitting first and second trainingpackets in a manner similar to the first embodiment. The process of stepS508 is to be executed when the training cycle is reached, or when thenumber of times of packet retransmission has exceeded the thresholdvalue.

Thus, according to a second embodiment of the present invention, apacket for which an acknowledgement has not been obtained can be sentagain. As a result, frame errors which occur in the presence of cyclicand local noise or cyclic and local impedance fluctuations can becorrected. Moreover, a training session is executed when the number oftimes of retransmitting packets has exceeded the threshold value. Thus,if the number of times of retransmission has become excessive, thetransmission/reception apparatus can promptly perform a training sessionto change the modulation method to one that is suitable for the currentstate of the transmission path. Furthermore, a training session is to beperformed when the training cycle is reached. Thus, by regularlymonitoring the state of the transmission path, thetransmission/reception apparatus can change the modulation method to asuitable one.

Third Embodiment

In the first embodiment, the receiving-end transmission/receptionapparatus of training packets returns to the transmitting-endtransmission/reception apparatus, as a channel estimation reply, an SNRanalytical result containing a tone map which dictates a greater one ofthe PHY rates calculated from two tone maps which are determined inresponse to two channel estimation requests. This enables communicationsto be performed at a maximum transmission rate which is in accordancewith the transmission path characteristics that exist at normal times.The above technique in the first embodiment is especially useful in thecase where the ratio of the periods of time of poor SNR characteristicsto the periods of time of good SNR characteristics is relatively small.

However, in the case where the ratio of the periods of time of poor SNRcharacteristics to the periods of time of good SNR characteristics isrelatively large, i.e., the transmission path characteristics are poor,problems may arise with the technique of the first embodiment. Thereason is that, in such a case, the period of time during which theactual PHY rate becomes maximum, i.e., the period of time during whichthe modulation parameter determined by using the technique of the firstembodiment matches the transmission path characteristics, is short, thusinviting increased errors.

Moreover, in a tone map which dictates a maximum PHY rate, modulationmethods with a high modulation level are assigned to a large number ofsub-carriers. As the modulation level increases, a higher SNR isrequired. Therefore, using a tone map which dictates a maximum PHY rateresults in a poor noise tolerance.

Thus, if a tone map which dictates a maximum PHY rate is used, errorsare likely to occur when the modulation parameters do not match thetransmission path characteristics during a data transmission, therebyresulting in a high retransmission rate. Therefore, a communicationperformed by using a tone map which dictates a maximum PHY rate does notnecessarily guarantee that a MAC rate (application rate), which is athroughput (amount of information processed in a predetermined period oftime) to be provided for an upper layer, is maximized.

Accordingly, in the third embodiment, a system which ensures a maximumMAC rate is proposed. FIG. 7 is a sequence diagram illustrating a flowof processes performed in a communication network system according tothe third embodiment of the present invention. Hereinafter, withreference to FIG. 7, a flow of processes performed in the communicationsystem according to the third embodiment will be described.

First, a transmission/reception apparatus which is to transmit trainingpackets transmits a channel estimation request packet RCE1PDU containinga first training packet to a receiving-end transmission/receptionapparatus (step S1). In response, the receiving-endtransmission/reception apparatus returns a channel estimation replypacket CER1PDU containing a first tone map to the transmitting-endtransmission/reception apparatus (step S2). Next, the transmitting-endtransmission/reception apparatus transmits a channel estimation requestpacket RCE2PDU containing a second training packet to the receiving-endtransmission/reception apparatus (step S3). In response, thereceiving-end transmission/reception apparatus returns a channelestimation reply packet CER2PDU containing a second tone map to thetransmitting-end transmission/reception apparatus (step S4). In thetransmitting-end transmission/reception apparatus, the period from stepsS1 to S4 defines a tone map acquisition period for acquiring a tone map.

After the tone map acquisition period, the transmitting-endtransmission/reception apparatus transmits a frame DATAPDU which isobtained by modulating input data using the first tone map (step S5).Next, the receiving-end transmission/reception apparatus checks forerrors in the frame DATA1PDU which is transmitted from thetransmitting-end transmission/reception apparatus, and upon detecting anerror, returns a response frame, with retransmission request informationcontained therein, to the transmitting-end transmission/receptionapparatus (step S6). Having received the response frame, thetransmitting-end transmission/reception apparatus analyzes the contentof the response frame, and if retransmission request information isfound therein, retransmits the frame. The transmitting-endtransmission/reception apparatus and the receiving-endtransmission/reception apparatus repeat such exchanging of a packetDATA1PDU using the first tone map and a response frame, up to apredetermined number of times (steps S7,S8). After the above process,the transmitting-end transmission/reception apparatus calculates a dataretransmission rate for the case of using the first tone map as [packetretransmitting times÷(number of transmitted packets+packetretransmitting times)] (step S9).

After transmission/reception of packets using the first tone map, thetransmitting-end transmission/reception apparatus transmits a packetDATA2PDU which is obtained by modulating input data using the secondtone map (step S10). Next, the receiving-end transmission/receptionapparatus checks for errors in the frame DATA2PDU which is transmittedfrom the transmitting-end transmission/reception apparatus, and upondetecting an error, returns a response frame, with retransmissionrequest information contained therein, to the transmitting-endtransmission/reception apparatus (step S11). The transmitting-endtransmission/reception apparatus and the receiving-endtransmission/reception apparatus repeat such exchanging of a packetDATA2PDU using the second tone map and a response frame, up to apredetermined number of times (steps S12,S13). After the above process,the transmitting-end transmission/reception apparatus calculates a dataretransmission rate for the case of using the second tone map as [packetretransmitting times÷(number of transmitted packets+packetretransmitting times)] (step S14).

Next, the transmitting-end transmission/reception apparatus calculatesMAC rates to be obtained in the cases where the first and second tonemaps are used, and selects one of the tone maps which dictates thefaster MAC rate (step S15). Specifically, the transmitting-endtransmission/reception apparatus first calculates a PHY rate which isobtained by using the first tone map. Then, the transmitting-endtransmission/reception apparatus calculates the MAC rate to be obtainedin the case where the first tone map is used, by employing theretransmission rate calculated at step S9 (i.e., the retransmission ratein the case where data is actually transferred by using the first tonemap). The formula for calculating the MAC rate is [MAC rate=PHYrate×(1−retransmission rate)]. Similarly, the transmitting-endtransmission/reception apparatus calculates a PHY rate which is obtainedby using the second tone map. Then, in accordance with the aboveformula, the transmitting-end transmission/reception apparatuscalculates the MAC rate to be obtained in the case where the second tonemap is used, by employing the retransmission rate calculated at step S14(i.e., the retransmission rate in the case where data is actuallytransferred by using the second tone map). Then, the transmitting-endtransmission/reception apparatus selects one of the tone map whichdictates the higher MAC rate, and transmits the selected tone map to thereceiving-end transmission/reception apparatus (step S15). The periodduring which data is actually transferred to obtain retransmission ratesby using the first and second tone maps and MAC rates for the respectivetone maps are calculated to determine a tone map which dictates thehigher MAC rate will be referred to as a “tone map selecting period”.

By using the selected tone map, the transmitting-endtransmission/reception apparatus modulates data, and transmits a packetDATAPDU (steps S16,S18). In response, the receiving-endtransmission/reception apparatus returns a response frame (stepsS17,S19). The period during which data is transferred by using theselected tone map will be referred to as a “data transfer period usingthe selected tone map”.

Thus, according to the third embodiment, the transmitting-endtransmission/reception apparatus actually attempts data transfers byusing two tone maps, thereafter selects a tone map which dictates amaximum MAC rate, and performs a data transfer. Therefore, the data canbe transferred with few errors. Thus, modulation parameters whichprovide an optimum communication efficiency can be selected.

The above embodiment illustrates an example where the selectingcondition for the tone map is that one which dictates a maximum MAC rateas calculated by using the above formula is selected. However, theselecting condition is not limited thereto. The selecting condition maybe any selecting condition by which a tone map that dictates a maximumthroughput to be provided for an upper layer is selected.

In the above embodiment, a tone map which provides a maximum MAC rate isselected. Alternatively, it is applicable to switch between a trainingsession for selecting a tone map which dictates a maximum PHY rate and atraining session for selecting a tone map which dictates a maximum MACrate as necessary, in accordance with the transmission pathcharacteristics, e.g., temporal characteristics of SNR. FIG. 8 is aflowchart illustrating an operation of a transmitting-endtransmission/reception apparatus in the case where the apparatusswitches between a training session for selecting a tone map whichdictates a maximum PHY rate and a training session for selecting a tonemap which dictates a maximum MAC rate. Hereinafter, with reference toFIG. 8, an operation of the transmitting-end transmission/receptionapparatus in the case of switching between a training session forselecting a tone map which dictates a maximum PHY rate and a trainingsession for selecting a tone map which dictates a maximum MAC rate willbe described.

First, the transmission/reception apparatus performs a training sessionin a manner similar to the first embodiment to select a tone map whichdictates a maximum PHY rate (step S301). Then, thetransmission/reception apparatus transmits data which is modulated byusing the tone map selected at step S301 (step S302).

Next, the transmission/reception apparatus determines whether thetraining cycle has been reached or not (step S303). If the trainingcycle has been reached, the transmission/reception apparatus returns tothe process of step S301 and performs a training session.

On the other hand, if the training cycle has not been reached, thetransmission/reception apparatus determines whether it would be betterto switch to selecting a tone map which dictates a maximum MAC rate(step S304). Specifically, the transmission/reception apparatusdetermines that it is better to switch to selecting a tone map whichdictates a maximum MAC rate if the packet retransmission rate has areached a predetermined value or more, or if the number of missingresponses has reached a predetermined value or more.

When determining that it is unnecessary to switch to using a tone mapwhich dictates a maximum MAC rate, the transmission/reception apparatusreturns to the process of step S302. On the other hand, when determiningthat it is better to switch to using a tone map which dictates a maximumMAC rate, the transmission/reception apparatus performs a trainingsession to select atone map which dictates a maximum MAC rate (stepS305), and proceeds to the process of step S306. Specifically, as shownin FIG. 7, the transmission/reception apparatus may acquire first andsecond tone maps during a tone map acquisition period; actually transmitdata by using the first and second tone maps during a tone map selectingperiod; based on the result of transmission, calculate actual MAC rates;and transmit data using by using a tone map which dictates a maximum MACrate during a data transfer period.

At step S306, the transmission/reception apparatus transmits data whichis modulated by using the tone map selected at step S305.

Next, transmission/reception apparatus determines whether the trainingcycle has been reached (step S307). If the training cycle has beenreached, the transmission/reception apparatus returns to the process ofstep S305.

On the other hand, if the training cycle has not been reached, thetransmission/reception apparatus determines whether it would be betterto switch to using a tone map which dictates a maximum PHY rate (stepS308). Specifically, the transmission/reception apparatus determinesthat it is better to switch to selecting a tone map which dictates amaximum PHY rate if the packet retransmission rate is less than apredetermined value.

If it is determined at step S308 that it is better to switch to using atone map which dictates a maximum PHY rate, the transmission/receptionapparatus returns to the process of step S301. On the other hand, if itis determined unnecessary to switch to using a tone map which dictates amaximum PHY rate, the transmission/reception apparatus returns to theprocess of step S306.

Thus, by switching between a training session for selecting a tone mapwhich dictates a maximum PHY rate and a training session for selecting atone map which dictates a maximum MAC rate, it becomes possible toselect an optimum tone map in accordance with the state of thetransmission path. Since a tone map which dictates a maximum PHY rate isselected first, in the case where the state of the transmission path hasnot worsened, a tone map can be promptly determined in a trainingsession.

Although an example is illustrated above where the aforementionedoperation is performed to select a tone map at the time of newlyinstalling a transmission/reception apparatus, the aforementionedoperation may be regularly performed so as to select a tone map whenevernecessary.

Fourth Embodiment

In the first to third embodiments above, the transmission/receptionapparatus selects, from among two tone maps obtained in response to twochannel estimation requests, a tone map which defines carriers to beused and/or modulation parameters for the respective carriers. Accordingto a fourth embodiment of the present invention, thetransmission/reception apparatus performs three or more channelestimations to acquire three or more tone maps, and from among theacquired tone maps, a tone map which dictates a maximum PHY or MAC rateis selected as described in the first to third embodiments. The blockstructure of the transmission/reception apparatus of the fourthembodiment is identical to that in the first embodiment, and thereforeFIG. 1 will be relied on in the following description.

FIGS. 9A, 9B, and 9C are graphs illustrating the effects obtained byperforming three or more channel estimations. Referring to FIG. 9A to9C, effects obtained when performing three or more channel estimationswill be described.

In FIG. 9A to 9C, the horizontal axis represents time, and the verticalaxis represents cyclic noise or SNR for a frequency at which the SNRfluctuates due to impedance fluctuations. With reference to thesefigures, the relationship between channel estimation timing and theresultant SNR will be discussed.

FIG. 9A is a graph illustrating channel estimation timing in the casewhere two channel estimations are to be performed. In FIG. 9A, it isassumed that the period during which SNR is deteriorated is shorter thanthe period during which SNR is not deteriorated. In FIG. 9A, a firstchannel estimation timing (as shown by “1” in a triangular frame in thefigure) coincides with the timing with which SNR deteriorates. A secondchannel estimation timing (as shown by “2” in a triangular frame in thefigure) does not coincide with the timing with which SNR deteriorates.In the exemplary case shown in FIG. 9A, by using a tone map acquiredthrough the second channel estimation, it is possible, even on atransmission path plagued with transmission path characteristicsfluctuations, to prevent decrease in speed due to performing acommunication using modulation parameters associated with low modulationspeeds.

In the case where a plurality of devices causing cyclic fluctuations inthe transmission path characteristics are connected to the transmissionpath, SNR characteristics as shown in FIG. 9B will be obtained. In theSNR characteristics as shown in FIG. 9B, each period during which SNR isdeteriorated is prolonged than in the case shown in FIG. 9A. Therefore,given the SNR characteristics as shown in FIG. 9B, even if two channelestimations are performed (as shown by the timings “1” and “5” intriangular frames in the figure), both of the first and second timingsmay still coincide with the timing with which SNR deteriorates. In thiscase, appropriate modulation parameters cannot be selected for thetransmission path characteristics which cyclically fluctuate over time.

Moreover, due to the influence of abrupt noise or the like, cyclicallyfluctuating SNR deteriorations and abrupt SNR deteriorations may existas shown in FIG. 9C. In this case, the timing of an abrupt SNRdeterioration may coincide with the channel estimation timing (as shownby “5” in a triangular frame in the figure). As a result, both of thefirst and second timings (as shown by the timings “1” and “5” intriangular frames in the figure) may coincide with the timing with whichSNR deteriorates. In this case, appropriate modulation parameters cannotbe selected for the transmission path characteristics which cyclicallyfluctuate over time.

Accordingly, in the fourth embodiment, three or more channel estimationsare performed. FIGS. 9B and 9C illustrate examples where five channelestimations are performed. As shown in FIGS. 9B and 9C, as a result ofperforming five channel estimations, the transmission/receptionapparatus can acquire a tone map through a channel estimation which wasperformed at a timing with which SNR did not deteriorate. Therefore,from among the five tone maps obtained, the transmission/receptionapparatus can select a tone map which dictates a maximum PHY or MACrate, in a manner similar to the first to third embodiments. In FIG. 9B,the tone maps obtained at timings “3” and “4” are the tone maps whichare obtained through channel estimations which were performed at atiming with which SNR did not deteriorate. In FIG. 9C, the tone mapsobtained at timings “2”, “3” and “4” are the tone maps which areobtained through channel estimations which were performed at a timingwith which SNR did not deteriorate.

Thus, in the presence of cyclic noise, or in the case where a pluralityof devices causing impedance fluctuations in the transmission pathcharacteristics are connected to power line, or in the presence ofabrupt noise/impedance fluctuations, the transmission/receptionapparatus performs three or more channel estimations. As a result, itbecomes possible to select an even more appropriate tone map than in thecase where tone maps are obtained through two channel estimations,without being influenced by prolongation of the periods during which SNRis deteriorated or abrupt fluctuations in the transmission pathcharacteristics, whereby high speed transmission can be realized.Depending on the degree of fluctuations in the transmission pathcharacteristics, the transmission/reception apparatus may dynamicallyvary the number of channel estimations to be performed or intervalstherebetween, thus further enhancing the effects of the presentinvention.

FIG. 10 is a flowchart illustrating an operation of atransmission/reception apparatus which transmits training packets duringa training session according to the fourth embodiment. Hereinafter, withreference to FIG. 10, an operation of the transmission/receptionapparatus which transmits training packets during a training sessionaccording to the fourth embodiment will be described.

First, the transmitting-end communication control section 1 of thetransmitting-end transmission/reception apparatus sets a transmissioncycle Ttr0 [seconds] as a time interval between transmissions oftraining packets (step S1301). The transmission cycle Ttr0 [seconds] isneither an integer multiple of the cycle of the commercial electricpower nor an integer multiple of half the cycle of the commercialelectric power. In other words, the time interval between two adjacentinstances of the channel estimation algorithm to be executed is unequalto the cycle of the quality fluctuations on the power line, and is equalneither to an integer multiple of the cycle of the commercial electricpower nor to an integer multiple of half the cycle of the commercialelectric power.

Next, the transmitting-end communication control section 1 sets atimeout time Ttot [seconds] (step S1302).

Next, the transmitting-end communication control section 1 transmits ani^(th) training packet (step S1303), where i is a positive integer whoseinitial value is one. The i^(th) training packet has identificationinformation added thereto, which can be used at a receiving end toconfirm that it is the i^(th) training packet.

Next, the transmitting-end communication control section 1 determineswhether the transmission of an N^(th) training packet has been completed(step S1304). If it has been completed, the transmitting-endcommunication control section 1 proceeds to the process of step S1308.On the other hand, if it has not been completed, the transmitting-endcommunication control section 1 proceeds to the process of step S1305.

At step S1305, the transmitting-end communication control section 1resets and starts a transmission cycle counter for measuring time todetermine whether the transmission cycle has been reached (step S1305).

Next, by referring to the transmission cycle counter, thetransmitting-end communication control section 1 determines whether thetransmission cycle Ttr0 [seconds] has passed or not (step S1306). Thetransmitting-end communication control section 1 repeats the process ofstep S1306 until the transmission cycle Ttr0 [seconds] has passed. Ifthe transmission cycle Ttr0 [seconds] has passed, the transmitting-endcommunication control section 1 proceeds to the process of step S1307.

At step S1307, the transmitting-end communication control section 1increments i by one, and returns to the process of step S1303 totransmit a next training packet.

At step S1308, the transmitting-end communication control section 1resets and starts a timeout counter for measuring time to determinewhether the timeout time has passed (step S1308).

Next, by referring to the timeout counter, the transmitting-endcommunication control section 1 determines whether the timeout time Ttot[seconds] has passed or not (step S1309). If the timeout time Ttot[seconds] has passed, the transmitting-end communication control section1 sets i=1 (step S1311), and returns to the processes of steps S1303 andthe subsequent steps to retransmit the first to N^(th) training packets.On the other hand, if the timeout time Ttot [seconds] has not passed,the transmitting-end communication control section 1 proceeds to theprocess of step S1310.

At step S1310, the transmitting-end communication control section 1determines whether the receiving-end communication control section 7 hasreceived an SNR analytical result from the counterpartingtransmission/reception apparatus and whether the received SNR analyticalresult has been notified to the SNR analytical results/acknowledgementnotifying section 8. If an SNR analytical result has not been received,the transmitting-end communication control section 1 returns to theprocess of step S1309. On the other hand, if an SNR analytical resulthas been received, the transmitting-end communication control section 1ends the process. Thereafter, based on the received SNR analyticalresult, the transmitting-end communication control section 1 allocatesinput data to the QAM encoder sections 2, and transmits packets.

FIG. 11 is a flowchart illustrating an operation of atransmission/reception apparatus which receives training packets duringa training session according to the fourth embodiment. Hereinafter, withreference to FIG. 11, an operation of the transmission/receptionapparatus which receives training packets during a training sessionaccording to the fourth embodiment will be described.

First, upon receiving an i^(th) training packet (step S1319), thereceiving-end communication control section 7 in the receiving-endtransmission/reception apparatus begins the following operation. Notethat the receiving-end communication control section 7 determineswhether the transmitted packet is an i^(th) training packet or not basedon the identification information which is added to the i^(th) trainingpacket.

Next, the receiving-end communication control section 7 determineswhether the received packet is the first training packet or not (stepS1320). If it is the first training packet, the receiving-endcommunication control section 7 sets a timeout time Ttor [seconds] (stepS1322), and proceeds to the process of step S1321. On the other hand, ifthe received packet is not the first training packet, the receiving-endcommunication control section 7 proceeds to the process of step S1321.

At step S1321, the receiving-end communication control section 7evaluates the SNR of the received training packet.

Next, the receiving-end communication control section 7 stores theevaluation result of the SNR of the i^(th) training packet obtained atstep S1321 to the SNR evaluation result storage section 9, as an i^(th)SNR evaluation result (step S1323).

Next, the receiving-end communication control section 7 resets andstarts a timeout counter for measuring time to determine whether thetimeout time has passed (step S1324).

Next, by referring to the timeout counter, the receiving-endcommunication control section 7 determines whether the timeout time Ttor[seconds] has passed or not (step S1325). If the timeout time Ttor[seconds] has passed, the receiving-end communication control section 7ends the process. On the other hand, if the timeout time Ttor [seconds]has not passed, the receiving-end communication control section 7proceeds to the process of step S1326.

At step S1326, the receiving-end communication control section 7determines whether an N^(th) training packet is being received or not.If an N^(th) training packet is not being received, the receiving-endcommunication control section 7 returns to the process of step S1325. Onthe other hand, if an N^(th) training packet is being received, thereceiving-end communication control section 7 proceeds to the process ofstep S1327.

At step S1327, the receiving-end communication control section 7determines a tone map for each of the first to N^(th) SNR evaluationresults stored in the SNR evaluation result storage section 9. Bycomparing all such tone maps, the receiving-end communication controlsection 7 selects an SNR evaluation result which dictates the fastestPHY rate.

Next, as an SNR analytical result, the receiving-end communicationcontrol section 7 transmits the SNR evaluation result selected at stepS1327 to the transmission/reception apparatus which has transmitted thetraining packet (step S1328), and ends the process. Based on thereceived SNR analytical result, the transmission/reception apparatuswhich has transmitted the training packet allocates input data to theQAM encoder sections 2, and transmits packets.

In FIG. 10 and FIG. 11, steps S1303 to S1306 and steps S1319 to S1324correspond to the i^(th) instance of the channel estimation algorithm.

Thus, according to the fourth embodiment of the present invention, thetransmission/reception apparatus performs three or more channelestimations. Therefore, it becomes possible to select an even moreappropriate tone map than in the case where tone maps are obtainedthrough two channel estimations, without being influenced byprolongation of the periods during which SNR is deteriorated or abruptfluctuations in the transmission path characteristics, whereby highspeed transmission can be realized.

In the fourth embodiment, too, data may be retransmitted in a manner asdescribed in the second embodiment.

The fourth embodiment illustrates an example where an SNR evaluationresult map which dictates a maximum PHY rate is selected. Alternatively,as described in the third embodiment, a tone map may be determined byselecting an SNR evaluation result which dictates a maximum MAC rate.Specifically, during a tone map acquisition period, the transmitting-endtransmission/reception apparatus may receive first to N^(th) tone maps,which are obtained with the first to N^(th) training packets, from thereceiving-end transmission/reception apparatus each time one of thefirst to N^(th) training packets is transmitted, and keep a record ofthe first to N^(th) tone maps. Then, during a tone map selecting period,the transmitting-end transmission/reception apparatus may actuallytransmit data modulated using the first to N^(th) tone maps acquiredduring the tone map acquisition period, while recording the number oftimes of packet retransmission, and calculate and record a MAC rate foreach tone map in a manner similar to the third embodiment. Then, thetransmitting-end transmission/reception apparatus may determine a tonemap which dictates a maximum calculated MAC rate, and transfer data byusing the tone map during a data transfer period.

Note that the transmitting-end transmission/reception apparatus mayreceive tone maps for N training packets from the receiving-endtransmission/reception apparatus; rank the received tone maps in adescending order of total modulation speeds of the carriers; nominatetone maps whose ranks are higher than a predetermined rank asprospective tone maps to be selected; perform actual communicationsusing the prospective tone maps; and select a tone map which dictates amaximum MAC rate from among the prospective tone maps. Thus, it becomesunnecessary for the transmitting-end transmission/reception apparatus toperform actual communications by using all tone maps, thereby making itpossible to change the carriers to be used and/or the modulationparameters for each carrier in a more rapid response to the transmissionpath characteristics fluctuations.

In the fourth embodiment, too, it is possible to switch between atraining session for selecting a tone map which dictates a maximum PHYrate and a training session for selecting a tone map which dictates amaximum MAC rate, as illustrated in FIG. 8.

Note that, in the second to fourth embodiments above, it is assumed thatQAM is used as a modulation scheme, but it is not limited thereto. Forexample, BPSK, QPSK, PAM, or ASK modulation may be used as a modulationscheme. In the case where PAM is used as a modulation scheme, thetransmission/reception apparatus will employ a DWT (Discrete WaveletTransform) section and an IDWT (Inverse Discrete Wavelet Transform)section, in which a Wavelet function is used as a basis function inplace of a trigonometric function in an FFT section and an IFFT section.The effect of the present invention can also be obtained in such cases.

Although the above embodiments illustrate examples where a power line isemployed as a transmission path for connecting transmission/receptionapparatuses on a communication network system to each other, the presentinvention is not limited thereto. Any transmission path other than apower line, e.g., a wireless means or a cable for a cable LAN, may beemployed. In either case, it is to be ensured that the time intervalbetween two instances of the channel estimation algorithm to be executedis unequal to the cycle of quality fluctuations on the transmissionpath.

The above embodiments illustrate examples where SNR is analyzed as anindex representing a transmission quality on the transmission path ateach carrier frequency. However, any other index may be used so long asit represents a transmission quality on the transmission path.

Note that the above-described embodiments can be realized by causing aCPU to execute a program, which is able to cause a CPU to execute theabove-described procedure stored in a recording medium (a ROM, a RAM, ora hard disk, etc.). In this case, the program may be executed after itis stored in a storing device via a recording medium, or may be directlyexecuted from the recording medium. Here, the recording medium includesa ROM, a RAM, a semiconductor memory such as a flash memory, a magneticdisk memory such as a flexible disk and a hard disk, an optical disksuch as a CD-ROM, a DVD, and a BD, a memory card, or the like. The“recording medium” as mentioned herein is a notion including acommunication medium such as a telephone line and a carrier line.

Note that each functional block as shown in FIGS. 1 and 5 may berealized as an LSI, which is an integrated circuit. Each functionalblock may be separately constructed in a chip form, or may beconstructed in a chip form so that a portion or the entire portionthereof is included. The LSI may be referred to as an IC, a system LSI,a super LSI, or an ultra LSI, etc., depending on the degree ofintegration. Also, the method of integration is not limited to LSI, andmay be realized by a dedicated circuit or a general purpose processor.Also, an FPGA (Field Programmable GateArray), which is an LSI that canbe programmed after manufacture, or a reconfigurable processor enablingconnections and settings of the circuit cells in the LSI to bereconfigured may be used. Further, in the case where another integrationtechnology replacing LSI becomes available due to improvement of asemiconductor technology or due to the emergence of another technologyderived therefrom, integration of the functional blocks may be performedusing such a new integration technology. For example, biotechnology maybe applied to the above-described integration.

Hereinafter, an example to which each of the above-described embodimentsis applied will be described. FIG. 12 is a diagram illustrating theoverall structure of a system in the case where thetransmission/reception apparatus of the present invention is applied toa high-speed power line transmission. As shown in FIG. 12, thetransmission/reception apparatus of the present invention provides aninterface between a multimedia device such as a digital TV (DTV), apersonal computer (PC), and a DVD recorder, etc., and a power line. AnIEEE1394 interface, a USB interface, or an Ethernet (R) interface may beused as an interface between the multimedia device and thetransmission/reception apparatus of the present invention. As such, acommunication network system is configured to transmit digital data suchas multimedia data at high speed via a power line. As a result, unlikein a conventional cable LAN, it is possible to use a power line, whichhas already been installed in a home and an office, etc., as a networkline without the need for installation of a network cable. Thus, thepresent invention can be easily installed at low cost, therebysubstantially improving user-friendliness.

In the embodiment as shown in FIG. 12, the transmission/receptionapparatus of the present invention is used as an adapter for convertinga signal interface of an existing multimedia device to a power linecommunication interface. However, the transmission/reception apparatusof the present invention may be built into a multimedia device such as apersonal computer, a DVD recorder, a digital video, and a home serversystem. As a result, it is possible to perform data transmission betweenthe devices via a power cord of the multimedia device. It eliminates theneed for wiring to connect an adapter and a power line, an IEEE1394cable, a USB cable, and an Ethernet (R) cable, etc., whereby wiring canbe simplified.

Also, the network system using a power line can be connected to theInternet, a wireless LAN, and a conventional cable LAN via a routerand/or a hub. Thus, it is possible to extend a LAN system using thecommunication network system of the present invention without anydifficulty.

Also, communication data transmitted over a power line by a power linetransmission is received by an apparatus by directly connecting to apower line. As a result, it is possible to eliminate leakage andinterception of data, which become a problem of wireless LAN. Thus, thepower line transmission method is advantageous from a securitystandpoint. It will be understood that data transmitted over a powerline may be protected by an IPSec, which is an extended IP protocol,encryption of contents, other DRM schemes, and the like.

As such, it is possible to perform a high-quality power linetransmission of AV contents by realizing copyright protection by theabove-described encryption of contents, and by realizing a communicationnetwork system which allows communication parameters to be set so thatthe system can operate with a maximum communication rate without beingaffected by local noise/impedance fluctuations occurring therein, whichis an effect of the present invention.

The present invention makes it possible to perform high-speedcommunications on the order of tens of 10 Mbps to hundreds of Mbps on apower line, and is applicable to any field where LAN connections are tobe realized without the need to provide additional wiring, e.g.,Internet-compatible home network devices, Internet-connected homeappliances, local area networks, OA (Office Automation), FA (FactoryAutomation), and the like.

While the invention has been described in detail, the foregoingdescription is in all aspects illustrative and not restrictive. It isunderstood that numerous other modifications and variations can bedevised without departing from the scope of the invention.

1. A transmitting apparatus for transmitting input data to a receivingapparatus via a transmission path, comprising: a transmitting sectionconfigured to generate a first training signal and a second trainingsignal by modulating a plurality of carriers respectively havingdifferent frequencies and configured to transmit the first trainingsignal and the second training signal to the receiving apparatus forestimating transmission conditions on a channel that is fluctuatingcyclically; a receiving section configured to receive, from thereceiving apparatus, a first channel estimation result including a firsttone map which indicates a modulation method for each carrier and isdetermined based on the first training signal, and a second channelestimation result including a second tone map which indicates amodulation method for each carrier and is determined based on the secondtraining signal; a storage section configured to store the first tonemap and the second tone map; and a control section configured to controla timing of transmission of the second training signal such that a timeinterval between transmission of the first training signal andtransmission of the second training signal is asynchronous to a cycle ofchannel fluctuation, wherein the transmitting section transmits theinput data by modulating the plurality of carriers according to thefirst tone map or the second tone map stored in the storage section. 2.The transmitting apparatus according to claim 1, wherein, the controlsection is further configured to calculate a communication rate in aphysical layer when using each of the first tone map and the second tonemap, and configured to select one of the first tone map and the secondtone map that dictates a maximum communication rate as a tone map to beused in the transmitting section for transmitting the input data.
 3. Thetransmitting apparatus according to claim 1, wherein, the controlsection is further configured to calculate a throughput provided for anupper layer when using each of the first tone map and the second tonemap, and configured to select one of the first tone map and the secondtone map that dictates a maximum throughput as a tone map to be used inthe transmitting section for transmitting the input data.
 4. Thetransmitting apparatus according to claim 1, wherein, the first tone mapis derived by calculating a signal-to-noise ratio with respect to afrequency of each carrier, based on the first training signal, and byallocating, for any carriers having a signal-to-noise ratio which isequal to or greater than a predetermined threshold value, a modulationmethod in accordance with a value of each signal-to-noise ratio, and byensuring that any carriers having a signal-to-noise ratio which is lessthan the predetermined threshold value is not used, and the second tonemap is derived by calculating a signal-to-noise ratio with respect tothe frequency of each carrier, based on the second training signal, andby allocating, for any carriers having a signal-to-noise ratio which isequal to or greater than the predetermined threshold value, andmodulation method in accordance with the value of each signal-to-noiseratio, and by ensuring that any carriers having a signal-to-noise ratiowhich is less than the predetermined threshold value is not used.
 5. Thetransmitting apparatus according to claim 1, wherein the transmittingsection is further configured to retransmit data if the data is notcorrectly received by the receiving apparatus.
 6. The transmittingapparatus according to claim 1, wherein, the transmission path is apower line through which commercial electric power is transmitted, andthe control section is further configured to control the timing oftransmission of the second training signal such that a time intervalbetween transmission of the first training signal and transmission ofthe second training signal is asynchronous to an integer multiple ofhalf a cycle of the commercial electric power.
 7. A transmitting method,executed by a transmitting apparatus, for transmitting input data to areceiving apparatus via a transmission path, the transmitting methodcomprising: generating a first training signal and a second trainingsignal by modulating a plurality of carriers respectively havingdifferent frequencies for estimating transmission conditions on achannel that is fluctuating cyclically; controlling a timing oftransmission of the second training signal such that a time intervalbetween transmission of the first training signal and transmission ofthe second training signal is asynchronous to a cycle of channelfluctuation; transmitting the first training signal and the secondtraining signal to the receiving apparatus; receiving, from thereceiving apparatus, a first channel estimation result including a firsttone map which indicates a modulation method for each carrier and isdetermined based on the first training signal, and a second channelestimation result including a second tone map which indicates amodulation method for each carrier and is determined based on thesecond'training signal; storing the first tone map and the second tonemap; and transmitting the input data by modulating the plurality ofcarriers according to the first tone map or the second tone map storedin the storing step.
 8. An integrated circuit to be used in atransmitting apparatus for transmitting input data to a receivingapparatus via a transmission path, comprising: a transmitting sectionconfigured to generate a first training signal and a second trainingsignal by modulating a plurality of carriers respectively havingdifferent frequencies and configured to transmit the first trainingsignal and the second training signal to the receiving apparatus forestimating transmission conditions on a channel that is fluctuatingcyclically; a receiving section configured to receive, from thereceiving apparatus, a first channel estimation result including a firsttone map which indicates a modulation method for each carrier and isdetermined based on the first training signal, and a second channelestimation result including a second tone map which indicates amodulation method for each carrier and is determined based on the secondtraining signal; a storage section configured to store the first tonemap and the second tone map; and a control section configured to controla timing of transmission of the second training signal such that a timeinterval between transmission of the first training signal andtransmission of the second training signal is asynchronous to a cycle ofchannel fluctuation, wherein the transmitting section transmits theinput data by modulating the plurality of carriers according to thefirst tone map or the second tone map stored in the storage section.